1. Field of the Invention
The present invention relates to an apparatus and method for delay time computation and delay compensation between a Base Station (BS) and a remote Radio Frequency (RF) unit in a broadband wireless access system. More particularly, the present invention relates to an apparatus and method for performing operations by achieving synchronization between a BS and a plurality of cascade remote RF units in a broadband wireless access system, irrespective of the number of remote RF units.
2. Description of the Related Art
A time delay factor of traffic data is very important in a Time Division Duplex (TDD) system such as a mobile-WiMax system. The time delay factor may be classified into two types. One is a data process delay time required until traffic data is output to an antenna after output from a modem of a Base Station (BS), and the other is a cable delay time depending on a length of a cable used to connect a BS modem card having a modem and a Radio Frequency (RF) unit when the BS modem card is remotely separated from the RF unit. The two types of delay time need to be correctly determined and compensated for, so that communication may be smoothly achieved between the BS and a Mobile Station (MS). More particularly, unlike the process delay time which is always constant after the system design is complete, the cable delay time is variable depending on an installation environment and a cable type, and thus delay time computation must be correctly performed on a real-time basis and must be correctly compensated for according to a desired system level.
FIG. 1 is a block diagram illustrating a BS modem card and a remote RF unit in a conventional broadband wireless access system.
As shown in FIG. 1, a BS modem card 100, equipped with a modem 101, is connected to a remote RF unit 140 via a cable. A signal output from the modem 101 is transmitted through an antenna 150 via the remote RF unit 140. A time for transmitting this signal must be equal to a time required when the signal output from the modem 101 is transmitted through an antenna 130 via an RF unit 120 included in a BS. Each of the RF unit 120 included in the BS and the remote RF unit 140 includes a transceiver module, an amplifier, and a filter.
At present, an interface mechanism between the BS modem card and the remote RF unit of the broadband wireless access system and a definition thereof are actively being discussed using a Common Public Radio Interface (CPRI) international standard. More particularly, a mechanism of delay time computation for each section between the BS modem card and the remote RF unit in a TDD system (e.g., mobile-WiMax) is defined in CPRI specification v3.0 revised in 2006.
However, since the mechanism disclosed in the CPRI and designed for delay time computation is a theoretical method, it is very difficult to select and determine a point of computation in the system. In addition, the number of computation blocks to be additionally implemented for computation is a plural number. Therefore, there is a need for a method for determining a delay time between the BS modem card and the remote RF unit by considering a practical design of the broadband wireless access system and a method for compensating for the delay time.